This invention relates in general to fatigue life estimation procedures and in particular to a method for obtaining fatigue life prediction information for a vehicle suspension component or similar article which is subjected to laboratory durability testing using real time loading.
Throughout the course of designing a new product, various testing and analysis procedures are often employed to determine the suitability of the product for its intended use. For convenience, the testing procedures are usually performed in a laboratory in such a manner as to closely simulate the service environment of the product. The nature and quantity of the testing procedures will, therefore, vary according to the nature of the product and its intended life span. For example, when the product is a vehicle suspension component, real time road simulation testing is usually performed. Such real time road simulation testing typically involves subjecting the suspension component to a series of loadings by means of a test device. The test loadings follow the magnitude and frequency content of the loadings which are expected to be received in the normal service environment of the vehicle.
Once testing has been performed on a particular product, the results thereof are analyzed so as to generate statistical inferences regarding the service life of the product. A known statistical procedure which has been used in the past to predict fatigue life is the Weibull analysis method. The Weibull analysis method requires that several samples of the product be subjected to identical testing procedures until some predetermined test termination criteria is met. The data which is acquired from each of those testing procedures is used in the Weibull analysis method to estimate the fatigue life of the product.
Unfortunately, the Weibull analysis method assumes that the amplitudes of the loadings applied to each of the tested samples of the product are constant over a period of time. This assumption is inconsistent with the actual use of many products, including vehicle suspension components, which are subjected to widely varying amplitude loadings during use. Thus, the Weibull analysis method has not been well suited for use in connection with real time road simulation testing and the data generated thereby to predict the fatigue life of vehicle suspension components.